This invention relates to a vehicle braking system for use in a vehicle such as an automobile.
In driving a vehicle, such as an automobile, it is sometimes desired to maintain braking force even though after a brake pedal is released, particularly, in stopping the vehicle on a sloped road or in frequent of stopping the vehicle due to a traffic jam. As such, there has been proposed some vehicle braking systems for automatically generating or maintaining the braking force in response to a predetermined condition. One example of prior art braking systems comprises a selector valve provided in a pipe line between a wheel brake and a master cylinder of the braking system for selectively permitting or intercepting the communication through the pipe line. By depressing a brake pedal hydraulic pressure is supplied to the wheel brake and, the selector valve is actuated by a predetermined operation such as the release of a depression force on the brake pedal, whereby the hydraulic pressure is maintained in the wheel brake even though the depression force on the brake pedal is released. Another example comprises a pneumatic booster interposed between the brake pedal and a master cylinder. The booster comprises a shell housing, a power piston displaceably mounted in the shell housing and partitioning the interior of the shell housing through a flexible diaphragm into a front vacuum chamber and a rear pressure chamber, and an output shaft connected to the power piston to actuate a piston of the master cylinder. Normally, atmospheric pressure is introduced into the pressure chamber by depressing a brake pedal and, the pressure introduced into the pressure chamber is exhausted to the vacuum chamber when the depression force on the brake pedal is released. At a predetermined operational condition the pressure in the pressure chamber is maintained even though the depression force on the brake pedal is released, whereby the wheel brake can be maintained at the braked condition.
Japanese Patent Publication No. 41838/1977 shows a pneumatic servo booster interposed between a brake pedal and a master cylinder of a hydraulic braking system of a vehicle, and an electromagnetic device connecting the brake pedal and an input rod of the booster. At a desired operating condition of the vehicle, the electromagnetic device acts to lock the input rod at an actuated condition automatically. The electromagnetic device requires a relatively large of electric power and the construction is complicated.
Japanese Utility Model Disclosure No. 60563/1983 shows a vehicle braking system comprising an electromagnetic device for electromagnetically locking a brake pedal at the braked position, a brake locking circuit for supplying a brake locking signal to the electromagnetic device at a predetermined condition, a seat sensor for generating a signal when the driver of the vehicle is not setting on a seat, an alarm for generating an alarm signal in receiving the brake locking signal and the seat signal, and a release circuit for releasing the brake locking circuit and the alarm in response to the actuation of a parking brake. The document does not show an embodiment of the electromagnetic device for locking the brake pedal, but, it is considered that the construction is complicated and the power consumption is relatively large.